The present invention generally relates to a radio station for transmitting and receiving digital information in a mobile communications system. More specifically, the present invention relates to a radio station for transmitting and receiving information having an antenna, at least one transmitting unit and at least one receiving unit.
Radio stations are used for transmitting information with the aid of electromagnetic waves. The frequency spectrum of the electromagnetic waves in question extends from a few kHz up to several hundred GHz. The frequency spectrum in the lower gigahertz range has gained importance as a result of the development of mobile radio technology. Radio stations at about 0.9 and 1.8 GHz are thus used for mobile radio technology. One example of a mobile communications system is the GSM mobile radio network (Global System for Mobile Communications), although such a mobile communications system is also implemented by known wire-free communications networks, for example in accordance with the DECT standard.
Where these radio stations are intended both for transmitting and receiving information, they have at least one receiving unit and at least one transmitting unit. The information to be transmitted is modulated in the transmitting unit onto a carrier frequency, and the transmitted signals generated are amplified. The receiving unit is used to evaluate the information in the received signals and to separate them from the carrier and from noise interference.
Such a radio station has been disclosed, for example, as a base station in German Patent Application 195 472 88.8. This radio station furthermore has an antenna for transmitting and receiving. Thus, not only are the transmitted signals transmitted, but the received signals are also received via this antenna. However, this radio station has the disadvantage that diversity reception is impossible.
Various options for implementing diversity reception have been disclosed in the document entitled "Short-Wave Telex and Data Transmission," L. Wiesner, Siemens AG, Third edition, 1980, pp. 94-104. The possibility of polarization diversity is proposed, inter alia, in which two antennas are used for diversity reception, one of which is polarized, for example, vertically and the other horizontally. Such an antenna system has also been disclosed in German Patent Specification DE 2 032 002 B2. These documents propose implementations for diversity reception which, however, are based on physically separated antennas and, in addition, do not take account of the problems of transmitting operation.
Conventional mobile communications systems, such as Siemens Function Specification, A30862-X1001-A314-03-7659, MOBNET, dated Aug. 25, 1995, page 5-2, also implement a radio station with diversity operation by having separate antennas for transmitting and for each individual diversity path. The two antennas for diversity reception must be physically separated to a certain extent, however, to ensure that the received signals are decorrelated. Another implementation option provides for duplexing of transmitted signals at the antennas for diversity reception. However, once again, the antennas must be physically separated for diversity reception here.
However, with regard to present-day mobile communications systems, there is considerable pressure on the network operators to manage with a small number of antenna sites. In this case, the provision of two separate antennas for diversity reception represents a considerable disadvantage.